Extraction of globular clusters members with Gaia DR2 astrometry

Abstract

In this work we present a method to identify possible members of globular clusters using data from Gaia DR2. The method consists of two stages: the first one based on a clustering algorithm, and the second one based on the analysis of the projected spatial distribution of stars with different proper motions. In order to confirm that the clusters members extracted by the method correspond to actual globular clusters, the spatial distribution, the vector point diagram of the proper motions and the colour-magnitude diagrams are analysed. We apply the developed method to eight clusters: NGC 1261, NGC 3201, NGC 6139, NGC 6205, NGC 6362, NGC 6397, NGC 6712 and Palomar 13; we show the number of members extracted, the mean proper motions derived from them and finally we compare our results with other authors. In order to analyse the efficiency of the extraction method we perform an estimation of the completeness and the degree of contamination of the extracted members.

BALRoGO: Bayesian Astrometric Likelihood Recovery of Galactic Objects – Global properties of over one hundred globular clusters with Gaia EDR3

“…Given the importance of a separation algorithm between such galactic objects and interlopers, Bustos Fierro & Calderón (2019) proposed a method based on Gaussian mixtures and clustering algorithms, with only one step not performed by a machine and applied it to eight GCs. Their work joined previous attempts to separate cluster members from interlopers through parametric and non-parametric methods (e.g., Vasilevskis et al 1965 andGaladi-Enriquez et al 1998, respectively).…”

The globular cluster M10: Reassessment of stellar membership, distance and age using its variable and HB stars

“…The Gaia-DR2 proper motions of the 9249 stars the FoV of our cluster images, for which we posses light curves, and the approach of Bustos Fierro & Calderón (2019) enable a cleaner version of the CMD. The isochrones from VandenBerg et al ( 2014) and the distribution of member stars near the turn-off point, suggest a cluster age of ∼ 13 Gyrs.…”

“…Using the high-quality astrometric data available in Gaia-DR2 (Gaia Collaboration et al 2018) and the method of Bustos Fierro & Calderón (2019), we were able to separate 21717 likely cluster members from a total of 36692 stars with Gaia-DR2 proper motions, in the field of radius 25 arcmin centered in the cluster. The corresponding Vector Point Diagram (VPD) is shown in Fig, 2, where it can be seen that the distribution of the proper motions of field and cluster stars (black and blue symbols in the figure) are not well separated, which implies that some contamination by field stars of our member stars list is likely to be present.…”

“…In this paper we describe our observations and data reductions as well as the transformation to the Johnson-Kron-Cousins photometric system ( § 2), we perform a search of new variables in our collection of light curves of stars in the FoV of the cluster, and report three new ones ( § 3). Using the proper motions in the Gaia-DR2 and the method of Bustos Fierro & Calderón (2019), we separate cluster members from field stars and discuss their effects on the Colour-Magnitude diagram (CMD) and the membership status of the variable stars ( § 4). A detailed identification of all known variables is carried out and the preparation of light curves is discussed ( § 5).…”

Ultraviolet Imaging Telescope (UVIT) observation of the Galactic Globular Cluster NGC 7492

“…Recent works use Gaia DR2 proper motion catalog to identify the cluster members in GGCs (Gaia Collaboration et al 2018b;Vasiliev 2019;Baumgardt et al 2019;Bustos Fierro & Calderón 2019). Generally, proper motions in RA (µ RA ) and DEC (µ DEC ) are used to separate out the contamination of field stars from the cluster members (Gaia Collaboration et al 2018b).…”